backend: upgrade to python 3.10
In 0e5519fe is eigenlijk alleen de .pre-commit-config.yaml van belang, want de rest is allemaal automatisch gedaan. Zie hier de upgrades: https://github.com/asottile/pyupgrade. Een tl;dr:
Optional[str] -> None | str
Union[int, str] -> int, str
typing.List -> list
typing.Dict -> dict
(and more imported from typing)
Closes #197 (closed)